Beobachtungen zur biologie und ultrastruktur der moosbewohnenden thekamöbe Nebela tincta (Rhizopoda)

Abstract

Summary The present paper includes observations on the population, the structure and ultrastructure of the shell and of the cyst, and the vertical distribution in the moss as well as observations on the excystment of Nebela tincta. The population of Nebela tincta in the moss Polytrichum formosum is characterized biometrically as a distinct group. The theca of Nebela tincta consists of innumerable siliceous platelets which are embedded into a layer of a homogeneous cement at the outside. The platelets are of different size and shape. They originate from various thecamoebean species, thus representing xenosomes in the theca of Nebela tincta. The platelet-pattern differs from theca to theca, not only with respect to platelet variety, but also in the extent of surface covering by the platelets. There is no indication towards a production of platelets by Nebela tincta itself. The stages of duration (cysts) are characterized by the plasma being motionless and rounded off within a homogeneous cystic membrane. The cystic membrane fastens the plasma to the plug by which the mouth of the theca is closed. This plug is composed of organic waste particles and more or less parallel layers of the same types of siliceous platelets which are used in the construction of the shell. The vertical distribution of Nebela tincta in the moss exhibits a maximum in the zone of decomposition of the green leaflets. Excystment occurs by uptake of water, rupture of the cystic membrane, and disintegration of the plug. Both the cystic membrane and the components of the plug are phagocytized. The possible functions of the lateral pores during encystment, excystment, and active life are discussed.